JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD MCA V DESIGN PATTERNS Previous Question Paper (January - 2018 - R13)

The Gang of Four (GoF) proposes two fundamental principles for creating robust object-oriented designs that prioritize flexibility and maintainability:

1. Program to an interface, not an implementation: This strategy encourages decoupling clients from specific classes by relying on abstract interfaces or base classes. By interacting with objects through their interfaces, the system remains independent of the concrete classes that implement them, allowing for easier substitution and extension.
2. Favor object composition over class inheritance: This principle suggests building complex functionality by assembling objects (composition) rather than extending existing classes (inheritance). Composition provides greater runtime flexibility, as the behavior of an object can be changed dynamically by replacing its components, whereas inheritance creates rigid, compile-time relationships that are harder to modify.

The Abstract Factory pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes. Its primary intent is to ensure that a system remains independent of how its products are created, composed, and represented.

Key aspects of the pattern include:

• Encapsulation of Creation: It isolates the concrete classes used by the client, as the client interacts only with the abstract interfaces of the products.
• Consistency: It ensures that a client uses objects from only one family at a time by grouping related products together within a single factory implementation.
• Interchangeability: Because the client code relies on abstract interfaces, concrete factory implementations can be swapped easily, allowing the entire family of products to be changed without modifying the client logic.